我想用灰色填充一定比例的绿色圆圈。我试图让灰色弧线占据60%的圆，但是它不起作用：

import javafx.application.Application;
import javafx.geometry.Orientation;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Arc;
import javafx.scene.shape.ArcType;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class CircleArc  extends Application {
    @Override
    public void start(Stage applicationStage) {
        ScrollPane scrollPane = new ScrollPane();
        scrollPane.setFitToWidth(true);

        FlowPane flowPane = new FlowPane();
        flowPane.setOrientation(Orientation.HORIZONTAL);

        Circle circle = new Circle(100);
        circle.setFill(Color.GREEN);
        Arc arc = new Arc(0, 0, 100, 100,
                -360 * 0.6, Math.toDegrees(0.6 * Math.PI));
        arc.setType(ArcType.ROUND);
        arc.setFill(Color.GRAY);

        Group group = new Group();
        group.getChildren().add(circle);
        group.getChildren().add(arc);

        flowPane.getChildren().add(group);

        scrollPane.setContent(flowPane);
        Scene scene = new Scene(scrollPane);
        applicationStage.setScene(scene);
        applicationStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

我做错什么了？